1. Technical Field
This invention relates generally to methods and devices for monitoring of structures and more particularly to use of dispersed sensing and signal processing modules adapted for attachment to structures such as airplane or spacecraft structural members. Such devices are particularly well suited for the detection and/or monitoring of fatigue cracks, corrosion, ice accretion, and structural damage associated with aircraft. The devices may also be employed to monitor strains in structures such as buildings, ships, underwater vessels, storage tanks, dams and bridges. Additionally, the devices may be used in an active mode in which the devices are excited electronically to generate forces that can be used in the control of structures, as well as to actuate, remove, or modify matter on the surface of the structure. These devices may also be applied to structures for use as intelligent switches or surface scanning devices.
2. Description of the Prior Art
A significant amount of effort and expense has been expended in the last few years in the field of aircraft testing and maintenance so as to provide the population with a safer means of travel. In light of disastrous aircraft crashes and the fatalities associated therewith which occur unnecessarily and all too often, and the concomitant ensuing liability suits, the future will surely include more stringent testing and maintenance procedures. See "Special Report: The World Airline Fleet Grows Older", Aviation Week and Space Technology, Vol. 131, No. 4 (Jul. 24, 1989) pp. 42-95.
Many aircraft crashes resulting from structural failure can be prevented by use of a health monitoring system which detects and monitors fatigue cracks, corrosion, ice accretion, as well as structural integrity. While recently developed technology has made some advances, even the most current systems require extensive modification of aircraft structure, cannot monitor large areas, are prone to misinterpretation, suffer from inaccuracy, are too complex, bulky and not self-contained, or require external power sources. Additionally, known systems are generally very limited in what they measure. For example, systems are known which detect ice formation on aircraft wings, however, they do not detect or monitor fatigue, cracks, corrosion, or structural integrity.
An on-line autonomous health monitoring system capable of monitoring a plurality of parameters is clearly desirable. Specific illustrative areas which will especially benefit from such a health monitoring system will now be discussed in detail sufficient to enable one to understand the context within which the present invention preferably operates and the problems which must be overcome.